Aluminum bronze alloy having improved resistance to intergranular oxidation by the addition of tin



United States Patent Oil MINUM BRONZE ALLOY HAVING IMPROVED RESISTANCE T INTERGRANULAR OXIDA- TION BY THE ADDITION OF TIN John F. Klement, Milwaukee, Wis., assignor to Ampco Metal, Inc., Milwaukee, Wis., a corporation of Wisconslu No Drawing. Application July '5, 1956 Serial No. 595,830

5 Claims. (Cl. 75-154) This invention relates to an aluminum bronze alloy having increased resistance to intergranular oxidation when subjected to stress in a hot water or steam atmosphere.

ing hot water and steam.

lt has been found that the oxidation or fracture of an aluminum bronze alloy under the action of stress and a hot water or steam corrodent, follow paths which are intergranular in natur. It is believed that the reason and are subject to oxidation.

The problem of intergranular attack serious in alpha-phase aluminum bronze alloys which contain about 5% to 8% aluminum. The alpha-phase alloy stances. However, the use has excellent working properties and can be readily fabricated into tube, sheet, plate, etc., in which form the alloy is often subjected to stress in a hot water or steam atmosphere. I

The present invention is based on the discovery that the resistance of an alpha-phase aluminum bronze alloy to heats of formation of tin oxides.

It has been found that it is necessary to make the improved alloy with a certain critical ratio of tin to the aluminum content. This is believed due to the additional theoretical consideration of the configurational entropy 2,829,968 Patented Apr. 8, 1958 Fice major and minor addition to copper and copper-base alloys in a great number of in- According to the invention the general composition range, by weight, of the alloy is as follows:

Aluminum 5.0 to 8.0%.

Iron 1.6 to 2.9%.

Tin In a weight ratio of 1 part tin to 11 to 32 parts of aluminum.

Copper Balance.

The controlled preferred compositional alloy is as follows, in weight percent:

Aluminum 6.00 to 6.75%.

Iron 2.00 to 2.40%.

Tin In a weight ratio of 1 part tin to 24 to 27 parts of aluminum.

Copper Balance.

A specific illustration of an alloy falling within the above ranges is as follows, in weight percent:

range of the Percent Aluminum 6.25 Iron 2.08 Tin 0.25 Copper 91.42

In addition to the ratio between the aluminum and tin, it has been found that the most desirable properties are nickel silicides are extremely brittle and tend to precipitate and gather at the grain boundaries. This tendency of the age hardening precipitate to gather at the grain boundary is believed to prevent the tin from gathering at the grain boundaries and ineifect destroys the purpose of the tin addition. The age hardening precipitates can be removed by a solution quench from over 1600 F., but a heat treatment such as this is not possible with a finished or fabricated article because the dimensional tolerances of the article will be destroyed by the heat treatment. Therefore, age be avoided in the present alloy.

The alloy is formed by initially preparing a pre-alloy of copper, aluminum and iron. This pre-alloy is then alloyed with additional copper and tin and cast. It is preferred not to add the tin to the pre-alloy because a portion of the tin would be lost by oxidation during melting and additional quantities of tin would have to be employed to hold the concentration of the same within the desired limits.

The present alloy can be made to provide a yield strength from 20,000 p. s. i. to 90,000 p. s. i., a tensile strength of 40,000 p. s. i. to 120,000 p. s. i. and an elongation in 2 inches of 1% to 60%, depending on the alloy composition, the method of fabrication employed and the heat treatment used. For example, an alloy having 6.25% aluminum, 2.10% iron, 0.25% tin and the balance copper, in the form of /2 inch thick plate, can be hot rolled and annealed to give a tensile strength of 85,000 p. s. i., a yield strength of 42,000 p. s. i., an elongation in 2 inches of 32% and a Brinell hardness of 160.

The same alloy in the form of cold drawn 1 inch diameter rod has a tensile strength of 90,000 p. -s. i., a yield strength of 70,000 p. s. i., an elongation in 2 inches of 30% and a Brinell hardness of 185.

As an example of the alloy as a weld deposit, the composition consisted of 7.0% aluminum, 2.4% iron, 0.25 tin and the balance copper. A sample of this alloy, taken through a butt welded joint, had a tensile strength of 75.000 p. s. i., a yield strength of 35,000 p. s. i., an elongation in 2 inches of 25% and a Brinell hardness of 150.

The alloy has high resistance to intergranular fracture resulting from oxidation at the grain boundaries. For example, the alloy will resist intergranular fracture for at least 2000 hours when stressed from 20,000 to 50,000 p. s. i. in a steam or hot water atmosphere at temperatures from 180 F. to 500 F. In some cases the alloy has been stressed for 8000 hours under the above conditions without failure.

As an example of the increased resistance of the alloy to intergranular oxidation when stressed in a hot water or steam atmosphere, a specimen of an alloy containing 6.00% aluminum, 2.20% iron, 0.24% tin and the balance copper was stressed beyond the yield strength by deflection bending in a media consisting of a aqueous solution of sodium hydroxide at a temperature of 350 F. The specimen did not fail in 1000 hours of testing.

A second specimen having a similar without tin, was stressed under identical conditions and failed after 100 hours of testing.

hardening constituents should.

composition, but

The present invention provides an aluminum bronze alloythat has greatly improved resistance to intergranular oxidation when stressed in steam and water atmospheres. The term steam is intended to include gaseous mixtures of steam and other vapors and the term hot water is intended to include heated aqueous solutions of salts, acids or bases and other materials containing water or moisture as an ingredient.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. An aluminum bronze alloy having increased resistance to intergranular oxidation when subjected to stress in a hot water or steam atmosphere, consisting essentially by weight of: about 5.0% to 8.0% aluminum; about 1.6% to 2.9% iron; tin in a weight ratio of 1 part tin to 11 to 32 parts of aluminum; and the balance substantially copper.

2. An aluminum bronze alloy consisting essentially by weight of: about 6.00% to 6.75% aluminum; about 2.00% to 2.40% iron; tin in a weight ratio of 1 part tin to 24 to 27 parts of aluminum; and the balance substantially copper, said alloy characterized by resistance to intergranular fracture for a period of at least 2000 hours when subjected to a stress in the range of 20,000 to 50,000 p. s. i. and a hot water or steam atmosphere at a temperature of F. to 500 F.

3. An aluminum bronze alloy having increased resistance to intergranular oxidation when subjected to stress in a hot water or steam atmosphere, consisting essentially of, by weight: about 5.0% to 8.0% aluminum; iron in a weight ratio of about 1 part iron to about 3 parts aluminum; tin in a weight ratio of about 1 part tin to 11 to 32 parts of aluminum; and the balance substantially copper, said tin segregating in the grain boundaries of the alloy and restricting the oxidation of said alloy at said grain boundaries.

4. An aluminum bronze alloy having increased resistance to intergranular oxidation when subjected to stress in a medium containing hot water or steam, consisting essentially of, by weight: about6.00% to 6.75% aluminum; iron in a weight ratio of about 1 part iron to about 3 parts aluminum; tin in a weight ratio of about 1 part tin to 24 to 27 parts of aluminum; and the balance substantially copper.

5. An aluminumbronze alloy, consisting essentially of, by weight: 6.25 aluminum, 2.08% iron, 0.25 tin; and the balance copper, said alloy having a high concentration of tin in the grain boundaries to thereby increase the resistance of the alloy to intergranular oxidation when subjected to stress in a medium containing hot water or steam.

2,031,315 Jennison Feb. 18, 1936 U. 8-. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF C QRRECTION I Patent No. 2,829,968 April 8, 1958 John F I Klement It is. hereby certified that error appears in the printed specification of the'above numbered patent requiring correction and that the said Let oers Patent should read as corrected below.

Column 2, line 4, for "complete" read ,--compete-.

Signed and sealed this 27th day of May 1958.

(SEAL) Attest:

KARL H, -AXLINE ROBERT C. WATSON Attesting Officer v Conmissioner of Patent: 

1. AN ALUMINUM BRONZE ALLOY HAVING INCREASED RESISTANCE TO INTERGRANULAR OXIDATION WHEN SUBJECTED TO STRESS IN A HOT WATER OR STEAM ATMOSPHERE, CONSISTING ESSENTIALLY BY WEIGHT OF: ABOUT 5.0% TO 8.0% ALUMINUM; ABOUT 1.6% TO 2.9% IRON; TIN IN AW WEIGHT RATIO OF 1 PART TIN TO 11 TO 32 PARTS OF ALUMINUM; AND THE BALANCE SUBSTANTIALLY COPPER. 